1. Field of the Invention
The present invention pertains to the art of measuring bioelectric signals and, more particularly, to a system for unobtrusively measuring bioelectric signals developed by an individual.
2. Discussion of the Prior Art
It is widely known that electric fields are developed in free space from many different sources. For example, organs in the human body, including the heart and brain, produce electric fields. For a variety of reasons, it is often desirable to measure these electric fields, such as in performing an electrocardiogram (ECG). Actually, the measuring of bioelectric signals can provide critical information about the physiological status and health of an individual, and are widely used in monitoring, evaluating, diagnosing and caring for patients. Basically, prior methods of measuring electric potentials associated with a human employ securing gel-coated electrodes directly to the skin of a patient. Obviously, this requires preparation and application time, while being quite discomforting to the patient.
More specifically, resistive electrodes have been predominantly employed in connection with measuring electric potentials produced by animals and human beings. As the resistive electrodes must directly touch the skin, preparation of the skin to achieve an adequate resistive connection is required. Such resistive electrodes are the standard for current medical diagnostics and monitoring, but the need for skin preparation and contact rule out expanding their uses. Although attempts have been made to construct new types of resistive electrodes, such as making an electrically conductive fabric, providing a miniature grid of micro-needles that penetrate the skin, and developing chest belt configurations for heart related measurements or elasticized nets with resistive sensors making contact via a conductive fluid for head related measurements, these alternative forms do not overcome the fundamental limitation of needing to directly contact the skin. This limitation leads to an additional concern regarding the inability to maintain the necessary electrical contact based on differing physical attributes of the patient, e.g. amount of surface hair, skin properties, etc.
Another type of sensor that can be used in measuring biopotentials is a capacitive sensor. Early capacitive sensors required a high mutual capacitance to the body, thereby requiring the sensor to also touch the skin of the patient. The electrodes associated with these types of sensors are strongly affected by lift-off from the skin, particularly since the capacitive sensors were not used with conducting gels. As a result, capacitive sensors have not been found to provide any meaningful benefits and were not generally adopted over resistive sensors. However, advances in electronic amplifiers and new circuit techniques have made possible a new class of capacitive sensor that can measure electrical potentials when coupling to a source in the order of 1 pF or less. This capability makes possible the measurement of bioelectric signals with electrodes that do not need a high capacitance to the subject, thereby enabling the electrodes to be used without being in intimate contact with the subject.
To enhance the measurement of bioelectric signals, there still exists a need for a system which can unobtrusively measure the signals with minimal set-up or preparation time. In addition, there exists a need for a bioelectric signal measuring system which is convenient to use, both for the patient and an operator, such as a nurse, doctor or technician. Furthermore, there exists a need for an effective bioelectric signal measuring system which can be used on a patient without the patient being cognitive of the system so as to require an absolute minimum intervention or assistance by the patient, particularly in situations wherein the patient cannot aid a nurse, doctor or the like, such as in the case of an infant or an unconscious individual. Specifically, a truly unobtrusive measurement system which does not require patient preparation is needed.